JPH03215384A - Crystal-growing device - Google Patents

Abstract

PURPOSE:To make possible to inhibit segregation without varying thickness of a melt layer nor adding any impurity by providing a crucible having a fixed shape opening to upward and growing crystal from the crucible. CONSTITUTION:The objective crystal-growing device is used in Czochralski method and a crucible 23 having upwardly opened shape receiving a solid layer 28 and a melt layer 27, and a heater 12 around the crucible, are provided in the device. A pulling-up shaft 14 is provided over said crucible 23 and a single crystal is pulled up. Then the opening shape of said crucible 23 is set so as a ratio of a weight variation of the melt to a total weight variation of grown crystal to coincide with a negative value of an efficient segregating coefficient of impurities about the melt layer 27, in a case that a thickness of the melt layer 27 is kept a constant.

Description

[Detailed Description of the Invention] L! The present invention relates to a crystal growth apparatus, and more particularly to an apparatus for growing a crystal such as a silicon single crystal used as a semiconductor material.

There are various methods for growing single crystals, one of which is a pulling method called the Czochralski method (CZ method). FIG. 5 is a schematic vertical cross-sectional view of a crystal growth apparatus used in the conventional pulling method, and 11 in the figure indicates a crucible. The crucible l1 is composed of an inner layer holding container 11a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 1lb made of graphite and also having a cylindrical shape with a bottom fitted on the outside of the inner layer holding container 11a. A resistance heating type heater 12 is arranged in a concentric cylindrical shape on the outside.

The crucible 11 is filled with a molten liquid 13 of the raw material melted by the heater 12, and a pulling shaft 14 made of a pulling rod or wire is placed on the central axis of the crucible 11.
is installed. A seed crystal 15 is attached to the tip of the pulling shaft 14, and when growing a single crystal, the seed crystal 15 is brought into contact with the surface of the melt 13 and the pulling shaft l4 is pulled up. A single crystal 16 formed by solidifying the melt 13 is grown.

By the way, when growing a semiconductor single crystal using this method,
In order to adjust the electrical resistivity and electrical conductivity type of the single crystal 16, impurity elements are often added to the melt 13 before pulling. For this reason, a phenomenon occurs in which the added impurities segregate along the crystal growth direction of the single crystal 16, and as a result,
There was a problem that a single crystal 16 having uniform electrical characteristics in the direction of crystal growth could not be obtained.

This segregation is determined by the ratio of the impurity concentration at the start of solidification to the impurity concentration at the end of solidification at a certain point in the single crystal, that is, the impurity concentration Cs in the single crystal that occurs at the interface between the melt and the single crystal during solidification. Ratio of impurity concentration cm in liquid Cs/Cl
．． That is, this occurs because the effective segregation coefficient Ke is not 1. For example, when Ke<1, as the single crystal 16 grows, the impurity concentration in the melt naturally increases, causing segregation in the single crystal 16.

A method for growing crystals while suppressing the segregation of impurities is a molten layer method. As shown in FIG. 6, the molten layer method uses a crucible 11 constructed similarly to the one shown in FIG.
By melting only the upper part of the raw material inside with the heater 12, the upper part becomes a molten liquid layer l7 and the lower part becomes a solid layer 18, and the impurity concentration in the molten liquid layer 17 is kept constant. This is a method of bringing the seed crystal 15 into contact and pulling up the pulling axis l4 to grow the single crystal l6.As a method of keeping the impurity concentration in the melt layer l7 constant, the constant melt layer thickness method and the melt layer thickness variation method are used. Proposed. For example, the constant molten layer thickness method is disclosed in Japanese Patent Publication No. 34-8242, Japanese Utility Model Publication No. 61-150862, Japanese Patent Publication No. 62-880, and Japanese Patent Application Publication No. 63-252989. 18 to form a molten liquid layer 17
In this method, the volume of the molten liquid layer 17 is kept constant, and impurities are continuously added during pulling of the single crystal 16, thereby keeping the impurity concentration in the molten liquid layer 17 constant.

In addition, in the molten layer thickness change method, the crucible 11 or the heater 12 is raised and lowered as the single crystal 16 grows, and the molten liquid layer 1 in the crucible 1l is
By changing the volume of 70, impurities can be removed from the single crystal 16
This is a method of keeping the concentration of impurities in the melt layer 17 constant without adding impurities during the pulling process. (Unexamined Japanese Patent Publication No. 61-205
No. 691, JP-A-61-205692, JP-A-61-
215285) In the above-mentioned constant melt layer thickness method, impurities are added continuously during the pulling of the single crystal l6, so in order to sufficiently suppress segregation, the impurities must be removed from the melt. It is necessary to diffuse the melt uniformly within the layer 17, and it is desirable to allow sufficient convection of the melt. However, when the melt is caused to convect, the inner layer holding container 11a made of quartz melts and oxygen is eluted. Since oxygen is contained in the grown single crystal l6 and becomes a cause of later crystal defects, convection must be suppressed, resulting in the problem of segregation occurring in the single crystal l6.

On the other hand, the melt layer thickness variation method does not require adding impurities during pulling of the single crystal 16, so it has the advantage of preventing segregation due to impurities not being sufficiently diffused into the melt. However, as described above, the volume of the molten liquid layer 17 using the cylindrical crucible l1 with a constant radius must be controlled by controlling the thickness of the molten liquid layer 17. The problem was that the volume of the layer 17 could not be controlled.

The present invention has been made in view of the above problems, and it is possible to easily control the volume of the melt layer without changing the thickness of the melt layer, and prevent segregation without adding impurities. The purpose is to provide crystal growth equipment. Solve the lesson. ．． In order to achieve the above-mentioned object, the crystal growth apparatus according to the present invention includes a crucible in which a solid layer and a molten liquid layer are formed, and a heat sink for melting the solid layer in the crucible is arranged around the crucible. In addition, in the crystal growth apparatus in which a pulling shaft is disposed above the crucible, the shape of the crucible is expanded upward, and the thickness of the molten liquid layer is kept constant. a crucible whose expanded shape is set so that the ratio of the weight change amount of the melt volume to the total weight change amount of the grown crystals matches the negative value of the effective segregation coefficient of impurities regarding the melt layer when the melt layer is maintained. It is characterized by having the following. According to the apparatus described above, when the pulling shaft is pulled up to grow crystals while keeping the thickness of the molten layer constant, the position within the crucible where this molten layer is formed changes and the shape of the crucible changes. Accordingly, the volume of the melt layer changes such that the ratio of the weight change amount of the melt amount to the total weight change amount of the grown crystals matches the negative value of the effective segregation coefficient of impurities regarding the melt layer. Therefore, the impurity concentration in the melt layer is kept constant, and the impurity concentration in the growing crystal does not segregate in the direction of growth and remains constant. The principle of the present invention will be explained below. In the state shown in FIG. 6, the upper part of the raw material filled in the crucible 11 is melted by a certain thickness by the hinita 12 and impurities are added, and then the raw material is directed from the upper side to the lower side. Regarding the mass balance of impurities in the state where the molten liquid 17 is pulled upward by the seed crystal 15 and solidified while being melted by the seed crystal 15 to grow the single crystal 16, if the diffusion of the impurities within the single crystal 16 is ignored, The following fil expression holds true. S 2"C・(g)dg+ C j (g・)・gj (g
・l = A ... (1) However, gs: Ratio of the total weight of the single crystal pulled to the total filling weight W of raw materials for single crystals and impurities Cs (gl: The melt in the single crystal when the ratio g is Impurity concentration C l (gs) at the contacting interface: Impurity concentration in the melt when the ratio is gs gβ (gs): Ratio of the weight of the melt in the crucible to W when the ratio is gs A: constant (11 Differentiating the expression with respect to gs, however, Cs(g
sl: Impurity concentration in the single crystal when the ratio is gs CR: Impurity concentration in the melt gR: The ratio of the weight of the melt to W, but the interface between the single crystal and the melt (hereinafter referred to as the solid-liquid interface)
Then, since Cs(gs) = Ke-(j(gs)-(31 (where Ke: effective segregation coefficient)) holds true, the above equation (2) becomes the following equation.

...(4) In this equation (4), dgj/dg in the first term on the left side
If s is dgj/dgs = −K e − (51, then crystal growth that makes gi zero is not substantially performed until the growth in the single crystal is completed, so gl/dgs in the second term on the left side is Ke does not become zero during crystal growth, resulting in dC s / dgs = O − (6).

Therefore, from equations (5) and (6) above, gt (ratio of melt weight in the crucible to W) changes in gs (ratio of total weight of pulled single crystal to W) at a certain point during single crystal growth. By matching the ratio of the amount of change in -Ke (negative value of the effective segregation coefficient), the amount of change in Cs (impurity concentration in the single crystal) relative to the amount of change in gs becomes zero, and segregation can be prevented. This is because there is a difference in impurity concentration at the solid-liquid interface based on the effective segregation coefficient Ke, and if the melt is not replenished from the start to the end of single crystal formation, the impurity concentration in the melt will gradually increase. However, by melting the unmelted raw material under the melt so that the ratio of the change in gt to the change in gs becomes -Ke, the impurity concentration in the melt is always kept constant, and This is because the impurity concentration in the single crystal is always maintained constant in the growth direction.

Therefore, if no impurities are added during the formation of quasicrystals, the amount of pulled and the amount of melt after starting pulling will be gQ. It is necessary to perform this so that gs satisfies equation (5).

On the other hand, when the thickness of the melt layer is L, the height from the bottom of the crucible is h, and the radius of the crucible is rfh), the following equation (7) holds true from equation (5).

Expanding this, r 2 (h + Ll − r ” (hl = K e−
r ” (h+L) ・(81.Here, r(h
Assuming that "l=A-B", equation (9) can be expressed as equation (lO).

6 Also, from the above assumption, it becomes r(0)-A, and A”
If r o is the radius of the bottom of the crucible, then the above assumption and (11
), the following equation is derived.

Therefore, by making the shape of the crucible such that it satisfies equation (12) and expands upward, if the thickness of the molten liquid layer is constant, the volume of the molten liquid layer increases as the crystal is pulled up (l
2) It will change so that the formula is satisfied. Therefore, even if the crystal is pulled up, if the thickness of the melt layer is kept constant, the impurity concentration in the melt layer will be kept constant, and the impurity concentration in the growing crystal will not be segregated in the growth direction. It becomes constant. DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the crystal growth apparatus according to the present invention will be described below with reference to the drawings. Note that components that have the same functions as those of the conventional example are given the same reference numerals. FIG. 1 is a schematic sectional view of a crystal growth apparatus according to the present invention, and numeral 21 in the figure indicates a chamber. The chamber 21 is a substantially cylindrical vacuum container with its axial direction perpendicular, and a crucible 23 is disposed approximately at the center of the chamber 21. The crucible 23 is composed of an inner layer holding container 23a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 23b made of graphite and having a cylindrical shape with a bottom fitted on the outside of the inner layer holding container 23a. As shown in Figure 2, it has an upwardly expanded shape. For example, if the impurity mentioned later is phosphorus,
Assuming that the thickness of the melt layer 27 is lOCII1, the height of the inner layer holding container 23a is 40 cm, and the diameter of the opening is 40 cm.
．． 0 cm, the diameter of the bottom is 17 cm, and the radius distribution is based on equation (l2). A shaft 29 for rotating and raising and lowering the crucible 23 is provided at the bottom of the outer layer holding container 23b of the crucible 23, and on the outer periphery of the crucible 23, a heater 12 consisting of an induction heating coil or the like can be raised and lowered. It is arranged. Furthermore, on the outside of the heater 12,
A heat insulating cylinder 30 is provided around the periphery so that the thicknesses of the molten liquid layer 27 and the solid layer 28 in the crucible 23 can be relatively adjusted by adjusting the relative vertical positions of the crucible 23 and the heater l2. It has become. On the other hand, above the crucible 23,
The pulling shaft 14 rotates through a small, generally cylindrical pull chamber 22 formed in the upper part of the chamber 21.
A seed crystal 15 is removably attached to the lower end of the pulling shaft l4. After immersing the lower end of the seed crystal 15 in the melt layer 27, the seed crystal 15 is raised while rotating.
The single crystal 16 is grown from the bottom end of the crystal 5. When operating the apparatus of the present invention configured in this manner, first, a lump or granular polycrystalline silicon is placed in the crucible 23 as a solid raw material in the necessary amount calculated backward from the volume of the single crystal 16 to be pulled. Fill it. Next, this solid raw material is melted from above by the heater 12, and
2 is lowered and heated until the thickness of the melt layer 27 becomes 10 cm, then phosphorus is introduced as an impurity and the phosphorus is diffused. Then, while the solid layer 28 is melted by temperature control and position control of the heater 12, the seed crystal 15 is added to the molten liquid layer 27 while maintaining the thickness of the molten liquid layer 27 at approximately 10 cm.
immerse the lower end of the container, and pull it up while rotating the pulling shaft 14. At this time, as the molten liquid layer 27 is pulled up, the volume of the molten liquid layer 27 is such that the ratio of the amount of change in weight of the molten liquid to the amount of change in the total weight of the grown crystals matches the negative value of the effective segregation coefficient of impurities regarding the molten liquid layer. change as it does. Therefore, the melt layer 27
The impurity concentration therein is kept constant, and a single crystal 16 with a constant impurity concentration can be grown from the lower end of the seed crystal 15. FIG. 4 shows the results of measuring the resistivity distribution of a silicon single crystal with a diameter of 6 inches and a length of about 40 cm grown using the above-mentioned apparatus. In Fig. 4, ○ indicates the resistivity distribution of silicon single crystal when using the crucible shown in Fig. 2, and ● indicates the resistivity distribution expanding upward as shown in Fig. 3. This shows the resistivity distribution of a silicon single crystal when using a crucible with a linear radius distribution. Furthermore, the broken line in the figure shows the resistivity distribution of a silicon single crystal formed by the conventional Czochralski method.

As is clear from FIG. 4, compared to the silicon single crystal formed by the conventional Czochralski method, the silicon single crystal formed using the apparatus according to the above embodiment has a higher resistivity due to the growth of the single crystal. It can be seen that the variation in the distribution is small within the range of ±10%, and segregation of impurities is prevented.

As is clear from the above description, the crystal growth apparatus according to the present invention includes a crucible in which a solid layer and a molten liquid layer are formed, and a heater that melts the solid layer in the crucible. In a crystal growth apparatus in which a crystal is disposed around the crucible and a pulling shaft is disposed above the crucible, the shape of the crucible is expanded upward, so that impurities are removed midway through the crystal growth apparatus. By keeping the thickness of the melt layer constant without adding it, it is possible to easily prevent the segregation of impurities in the single crystal. Furthermore, when the thickness of the melt layer is kept constant, the ratio of the weight change of the melt volume to the total weight change of the grown crystals matches the negative value of the effective segregation coefficient of impurities regarding the melt layer. When using a crucible with a shape that expands smoothly, by keeping the thickness of the molten liquid layer constant,
The impurity concentration in the melt layer can be kept accurately constant, and the impurity concentration in the growing crystal can always be kept constant in the crystal growth direction. Therefore, segregation of impurities can be prevented without changing the thickness of the melt layer, and the volume of the melt layer can be easily controlled.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical sectional view showing a crystal growth apparatus according to the present invention, FIG. 2 is a schematic sectional view showing an embodiment of a crucible,
FIG. 3 is a schematic cross-sectional view showing another embodiment of the crucible;
The figure is a graph showing the results of measuring the resistivity distribution of silicon single crystals formed by the apparatus of the present invention and the conventional method. Figures 5 and 6 are schematic vertical cross-sectional views of the apparatus used in the conventional crystal growth method. It is. 12... Heater 14... Pulling shaft 23...
Crucible 23a... Inner layer holding container 23b... Outer layer holding container 27... Molten liquid layer 28... Solid layer 1wi 9S Fig. 2 R base Fig. 5 ○

Claims (2)

[Claims] (1) A crucible is provided in which a solid layer and a molten liquid layer are formed, a heater for melting the solid layer in the crucible is disposed around the crucible, and a pulling shaft is disposed above the crucible. A crystal growth apparatus characterized in that the crucible shape is expanded upward. (2) When the thickness of the melt layer is kept constant, the ratio of the weight change of the melt volume to the total weight change of the growing crystal is
2. The crystal growth apparatus according to claim 1, further comprising a crucible whose expansion shape is set to match a negative value of an effective segregation coefficient of impurities regarding the melt layer.